At the present time, bone losses are generally filled using bone replacement materials, or autogenic or allogenic bone.
Examples of bone replacement materials include inorganic materials such as calcium phosphate, hydroxyapatite, or bioglass, which are replaced by bone after a long absorption period. However, this procedure may be used only for minor defects; otherwise, there is the risk of infection due to insufficient vascularization. The absorption of inorganic materials is inadequate. Such bone materials, i.e., bone replacement materials, do not emit biomechanical pulses and therefore do not initiate active regeneration. Also used are synthetically manufactured organic materials, such as polyesters, polyamino acids, polyanhydrides, polyorthoesters, polyphosphazenes, polylactides, or polyglycolides, or allogenic organic materials, for example of bovine origin. Material combinations of the various types of materials are also used as bone replacement composites. However, bone substance losses may also be compensated for using microvascular connected autogenic or allogenenically vascularized transplants. However, use of an allogenic bone replacement may trigger undesired immune reactions and transmit infection.
From a biological standpoint, the best replacement material for bone is an autologous spongiosa transplant. However, such transplants have limited availability and exhibit a high absorption rate after transplantation.
The materials and techniques used in the prior art frequently provide unsatisfactory bone quality, resulting, for example, in insecure anchoring of implant beds. In addition, frequently the bone replacement is insufficiently vascularized, thereby increasing the risk of infection. Furthermore, methods of the prior art often use growth factors which greatly increase the costs for the methods.
Instead of using a bone replacement, missing bone substance may sometimes be filled by bone regeneration. Segmented interruptions in the osseous continuity of long tubular bones may be treated in this manner by distraction osteogenesis.
Callus distraction has been known for over a hundred years. The most important biological stimulus for bone formation is mechanical stress. This releases piezoelectric forces which activate the osteoblasts and osteoclasts. Distraction osteogenesis induces new bone formation by triggering biological growth stimuli by means of slow separation of bone segments. This method achieves direct formation of woven bone by distraction. The defined tensile stress is essential for bone formation. When such a defined tensile stress is applied to bone fragments, the mesenchymal tissue exhibits an osteogenetic potential in the gap and at the contiguous fragment ends. When sufficient vascular potency is present, progressive distraction results in metaplasia of the organized hematoma, also referred to as blood coagulum, in a zone of longitudinally arranged fibrous tissue, which under optimal external and internal conditions may be directly converted to woven bone. A complication, however, is that the bone tissue requires highly complex control for regeneration.
WO 01/91663 describes a two-dimensionally oriented bone distraction using an artificial interface. For such distraction methods from the prior art, in many cases only vertical regeneration is possible, for example in the jaw region.
Thus, bone regeneration by distraction cannot be used for every type of bone defect. In addition, the devices used for distraction are complex, and distraction methods take a comparatively long time.